Handbook of air conditioning and refrigeration / Shan K

17.20 CHAPTER SEVENTEEN
TABLE 17.6 Minimum Duct Insulation R-Value, * Cooling and Heating Supply Ducts and Return Ducts
Duct location
Climate zone
Unvented
attic with
Unvented
attic with Indirectly
Envelop Ventilated backloaded roof Unconditioned conditioned
criteria table HDD65 CDD50 Exterior attic ceiling insulation space † space § Buried
Heating ducts only
5-1 to 5-7 0-1800 All None None None None None None None
5-8 to 5-12 1801-3600 All R-3.5 None None None None None None
5-13 to 5-15 3601-5400 All R-3.5 None None None None None None
5-16 to 5-18 5401-7200 All R-6 R-3.5 None None None None R-3.5
Cooling only ducts
5-15, 18, 20,
22 to 26
All 0-1800 R-1.9 R-1.9 R-1.9 R-1.9 R-1.9 None None
5-12, 14, 17,
19, 21
All 1801-3600 R-3.5 R-1.9 R-3.5 R-1.9 R-1.9 None None
5-7, 9, 11,
13, 16
All 3601-5400 R-3.5 R-3.5 R-6 R-1.9 R-1.9 None None
5-4, 6, 8, 10 All 5401-7200 R-6 R-6 R-6 R-3.5 R-1.9 None None
Combined heating and cooling ducts
5-9 1801-2700 0-5400 R-6 R-3.5 R-6 R-1.9 R-1.9 None
5-10 2701-3600 5401 � R-6 R-6 R-6 R-3.5 R-3.5 None
5-11 2701-3600 3601-5400 R-6 R-6 R-6 R-3.5 R-3.5 None
5-12 2701-3600 0-3600 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 None
5-13 3601-5400 3601 � R-6 R-6 R-6 R-3.5 R-3.5 None
5-14 3601-5400 1801-3600 R-6 R-3.5 R-6 R-1.9 R-3.5 None
5-15 3601-5400 0-1800 R-3.5 R-3.5 R-3.5 R-1.9 R-1.9 None
Return ducts
5-1 to 5-26 All climates R-3.5 R-3.5 R-3.5 None None None None
* Insulation R-values, measured in (h� ft 2 � °F)/Btu, are for the insulation as installed and do not include film resistance. The required minimum
thicknesses do not consider water vapor transmission and possible surface condensation. Where exterior walls are used as plenum walls, wall insulation
shall be as required by the most restrictive condition of 6.2.4.2 or Section 5. Insulation resistance measured on a horizontal plane in accordance
with ASTM C518 at a mean temperature of 75°F at the installed thickness.
† Includes crawl spaces, both ventilated and nonventilated.
§ Includes return air plenums with or without exposed roofs above.
Source: ASHRAE/IESNA Standard 90.1-1999. Reprinted by permission.
do not include air film resistances. The required minimum thickness does not consider water vapor
transmission and possible surface condensation. The recommended thickness of insulation layer, or
duct wrap, for R-3.5 h�ft 2 �°F/Btu (0.62 m 2 �°C/W) is 1 to 1.5 in. (25 to 38 mm), and for R-6
h�ft 2 �°F/Btu (1.06 m 2 �°C/W) is 2 to 3 in. (50 to 75 mm).
Exceptions of duct and plenum insulation include
● Factory-installed plenums, casings, and ductwork as part of the equipment
● Ducts or plenums located in heated spaces, semiheated spaces, or cooled spaces
● For runout less than 10 ft (3 m) in length to air terminals or air outlets, R-value of insulation need
not exceed R-3.5.
● Backs of air outlets and outlet plenums exposed to unconditioned or indirectly conditioned space
with face area exceeding 5 ft2 (0.5 m2 ) need not exceed R-2, for those 5 ft2 (0.5 m2 ) or smaller
need not be insulated.